USING IRRIGATION TO INCREASE CROP PRODUCTIONHistorically, irrigation has been an important agricultural technology with strong impact on crop productivity. On average,irrigated crop yields tend to be highter than those from unirrigated land (Lascano and Sojka, 2007), but there can also beunintended negative consequences of irrigation if it is not managed well including river and groundwater depletion and salinization.

Irrigation is useful in regions where the process of evaporation (E) and traspiration (T) (water loss from crop plants) exceedprecipitation or rainfall.

Factors that affect ET include:

ET estimations and deciding when to irrigate

A farmer can use a number of means forestimating ET and for scheduling irrigations:

• direct inspection or with a hand-push soil probe

• determine the available water holding capacity and the allowablewater depletion for your soil type and the crop you’re growingusing the “feel method”

• setup a water pan in the sun with the allowable soil waterdepletion marked below the initial water level, and irrigate whenthe water evaporates to the marked level, and

• access local weather and ET data from the internet

The effective root zone

The top half of the actual root zone usuallysupplies about 70% of the crop’s water needs.

T TE

E

ET = E+T

ET = evapotranspiration

E = evaporation T = transpiration

• climate: windspeed, temperature, humidtiy

• field aspect or solar exposure

• crop type

• stage of crop growth

• soil moisture

• soil cover

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

IRRIGATION SCHEDULING

How will you know when to irrigate and how much water to apply?

Monitoring moisture availability

• Crop stage of growth and vigor

• Air temperature and wind speed

• Rainfall or irrigation water applied

• Soil moisture

Calculations

• Daily crop water use or evapotranspiration

• Soil water balances and water available to plants

Wetting pattern of drip tape

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

ADDITIONAL POSSIBLE BENEFITS OF COVER CROPSWHEN USED AS SURFACE MULCHES

When cover crops are converted to surface mulches, or when crop residues are maintained on the soil, they may serve toreduce soil water evaporation and thereby conserve water for crop transpiration. Thus, by generating and maintaining residues,a farmer, tries to “take the ‘E’ out of ‘ET’, to increase crop water use efficiency.

Estimates of water savings due to reduced tillage and surface residues have been determined to be upwards of 10 cm duringa crop season in the US.

Onions growing in crop residueBrazil, 2005

Tomatoes growing in cover crop residueCalifornia, USA, 2008

Beans growing in crop residuesNebraska, USA, 2007

Measuring soil water evaporation underresidues and bare soilCalifornia, USA, 2009

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

USING COVER CROPS TO INCREASE CROP PRODUCTIVITYWhat are cover crops?Cover crops are legumes, cereals, or an appropriate mixture grown specifically to protect the soil against erosion; amelioratesoil structure; enhance soil fertility; and suppress pests, invading weeds, insects, and pathogens. When cover crops areconverted to a surface residue mulch, they can also serve to conserve soil water.

Because low soil fertility has been a major constraint hampering the productivity of Kenyan small holder farms, and becauselegumes can play a major role in improving farm productivity, the Legume Research Network Project (LRNP) has done a lotof work in Kenya over the past 15 years to introduce legume cover crops throughout the country.

How much Nitrogen can cover crops provide?

Vigorous cover crops can be produced byfollowing existing recommendations for speciesand variety selection,planting date, seedingrate, inoculation procedures and terminationdate. The amount of nitrogen a cover cropproduces depends entirely on the culturalpractices that are used.

kg N/ha production strategy

0 - 112

112 - 224

224 - 336

> 336

as easy as falling off a chair

follow existing recommendations

skill, time, favorable weather, and lots of seed

multiple top removal over extended time periods

Findings of the Legume Research Network Projectin Kenya 1995 - 1997

• greater crop yields with cover crop incorporation at most sites

• in semi-arid regions, mulching resulted in superior maize yieldsdue to moisture conservation,

• returns to labor were higher with incorporation than mulching

Estimating cover crop N content

• harvest 1 m2 of your cover corp

• weigh the fresh weight

• multiply the fresh weight times theconversion factor to get kg/ha

cover crop

clover (Trifolium)

bell bean (Vicia faba)

cowpea (Vigna unguiculata)

vetch (Vicia dasycarpa)

grass (average)

legumes (average)

48

37

44

59

23

40

conversionfactor (kg/ha)

(http://uric.ucdavis.edu/veginfo/topics/fertilier/fertguide.html)

carrot

corn

melon

onion

potato

squash

tomato

90 - 165

135 - 270

110 - 165

135 - 335

165 - 335

90 - 165

110 - 225

vegetable (kg/ha)

Typical Nitrogen needsof vegetable crops

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

WHAT ELSE MIGHT BE DONE TO IMPROVE CROP PRODUCTIVITY?

Consider organizing an “information collective”to share information

Keep an “institutional memory”

Connect with other regional and nationalagriculture information groups such as KARIand the Legume Research Network Program

Set goals and seek help with othertechnology tools

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

EVOLUTION OF AGRICULTURAL TECHNOLOGIES WITHSTRONG IMPACT ON AGRONOMIC PRODUCTIVITY

AND POPULATION CARRYING CAPACITY

Lal et al., 2007. Soil and Tillage Research 93(2007): 1-12.

Era

11000 - 9000 BC

9500 - 8800 BC

5000 - 4000 BC

3000 - 2000 BC

2500 - 2000 BC

900 - 700 BC

370 - 280 BC

1 AD

1604 - 1668 AD

1100 - 1200 AD

1803 - 1873 AD

1950 - 1970 AD

1960s AD

1980s AD

2000 AD

Mesopotamia

Sumerians

Mesopotamia

Indus Valley

Mespotamia

Greece

Rome

Rome

Germany

Moorish Spain

Germany

U.S. corn Belt

Israel

Beginning of settled agriculture

Use of supplemental irrigation

Use of simple tools such as an “ard” or plow

Use of animal-driven plow

The concept of fertility of cropland soils

Use of animal manure

Use of green manures

Use of lime and saltpeter (KNO3)

Impact of saltpeter on plant growth

Soil quality

Use of chemical fertilizers

Conservation tillage, no-till farming

Drip irrigation, fertigation

Biotechnology and GM crops

Deliver nutrients and water directly to plant roots,biomass-based H2 fuels, conservation tillage, land-saving technologies, precision farming, soil carbonsequestration

Locale Technology

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

s

WO R K G R O U

P

Conse

rvat

ion

Tillage and Cropping

System

sDr. Jeff MitchellCropping Systems SpecialistUniversity of California

mitchell@uckac.edu